1. Field of the Invention
The present invention relates to a header for a harvesting machine and in particular to a preformed header frame. When the header is supported above the ground intermediate the ends of the frame, loading of the frame deflects the ends of the frame to a position in which the cutterbar assembly along the frame front edge assumes a substantially straight and horizontal position.
2. Description of the Related Art
To increase harvesting efficiency, harvesting machines, such as combines, have increased in size and capacity over the years. With this increasing capacity, the detachable header used for picking a crop has increased in width as well. A wider header increases efficiency by reducing the number of passes through the field required by the harvesting machine to cover the entire field. However, the increased width of the header has resulted in increased difficulties in maintaining the cutterbar assembly at the front of the header in a straight orientation for proper operation. Headers are typically supported by the harvesting machine at a location in the middle of the header. When the header is suspended above the ground, the ends of the header tend to deflect downward under the load. As headers increase in width, it is harder to prevent this deflection. Deflection of the cutterbar assembly from a straight position will reduce the life of the knife back of the cutterbar assembly and the knife drive motor. In addition, if the ends of the cutterbar assembly are lower than the center portion, the reel will not be at a constant distance from the cutterbar across the entire length of the cutterbar assembly. Proper crop movement over the cutterbar will only occur over part of the header width.
Header manufacturers have taken various approaches to address this problem. One approach is to build a header frame with a main beam having multiple round tubes joined end to end with the center of the beam formed by larger tubes. A number of braces and gussets connect to the main beam to form a truss like structure to reduce the deflection. Another approach is to build a main beam in which lengthwise tube has a second tube placed thereon at a center portion of the longer tube. Gussets extending lengthwise from the ends of the second tube gradually reduce in section height toward the ends of the main beam. The individual pieces are welded together with the intent that the main beam will resist deflection under load. The use of gauge wheels at the outer ends of the header can also help control deflection.